The invention relates more particularly to a process for the radio transmission of coded data superimposed on a traditional frequency-modulated broadcast wherein coded data to be transmitted are modulated in a predetermined frequency range in order to create modulated coded signals. The modulated coded signals are mixed with the low-frequency signals of a traditional program to be broadcast by a frequency modulation radio transmitter, the signals delivered by a frequency modulation receiver are filtered in order to isolate the said modulated coded signals. The filtered, modulated coded signals are demodulated and the transmitted coded data are displayed or recorded by applying the demodulated, filtered coded signals to a display or recording unit.
A variety of systems for the radio transmission of coded data are already known. In general, these systems constitute warning or watching devices and require the existence of transmitters and receivers specially designed for the transmission of coded data.
Furthermore, attempts have already been made to superimpose, on a conventional radio broadcast, certain signals for controlling particular functions. However, applications of this type are very specific and do not permit the reception and display, in uncoded form, of coded data which are capable of complementing the content of audio data transmitted conventionally by radio waves.
It has also been proposed to superimpose coded data on a conventional frequency-modulated radio broadcast by adding a low-level subcarrier modulated by coded signals. However, the proposed systems have not as yet made it possible to obtain reliable transmissions without substantially impairing the main program or the additional coded signals.